A spunbond nonwoven is typically made from monofilaments of thermoplastic polymer. Because of their virtually endless length, these monofilaments differ from staple fibers that have for example much shorter lengths of 10 mm to 60 mm.
The nonwoven is made in a continuous process starting with spinning of the monofilaments by a spinneret. The still hot monofilaments, normally passing vertically downward, are then cooled in a cooler and then elongated in a stretcher downstream from the cooler. An intermediate passage connects the cooler to the stretcher downstream therefrom.
Various embodiments of an apparatus of this type are known in principle from practice. However, many of these known apparatuses have the disadvantage that the filaments often cannot be deposited satisfactorily to form the spunbond nonwoven. This results in irregularities in the form of defects in the spunbond nonwoven in deposition of the filament. The homogeneity of the spunbond nonwovens is more or less greatly impaired due to these defects. One cause of defects in the spunbond nonwoven are so-called drips, which result from tearing one or more filaments as well as the accumulations of melt thereby formed. These drips may result in formation of thick spots in the spunbond nonwoven. Such drips and/or defects in the spunbond nonwoven are usually larger than 2×2 mm. However, defects in the spunbond nonwoven also result from so-called “hard pieces” that come about as a result of a loss of tension in the spun filament. The filaments relax and recoil and thus form a cluster that sticks together because of the molten state of the filament. The resulting defects produced in the spunbond nonwoven in this way normally are less than 2×2 mm in size. However, they are usually tangible and/or visible. Such defects occur primarily at a throughput greater than 120 km/h/m and in particular at a throughput greater than 150 kg/h/m. Greater spinning-zone lengths also promote irregularities in the spunbond nonwovens.
There have already been attempts to reduce these problems by making the filament treatment more uniform. In particular there have been attempts to reduce the defects in spunbond nonwovens by means of more uniform cooling in the cooler. Especially at high throughputs however, these measures have been successful only to a limited extent. There is thus a need for improvement.